U.S. Pat. No. 4,814,883 to Perine et al. discloses a multiple input/output video switch for commercial insertion. FIG. 1 enclosed herewith illustrates a portion of the commercial insertion system described in the Perine patent. Video switches VS.sub.1, VS.sub.2 and VS.sub.n are respectively associated with channels 1 (CH1), channel 2 (CH2) and channel n (CHn). The video switches are located at the cable head end. At the head end, the cable system operator receives a plurality of programmed channel video signals, some of which are identified in FIG. 1 as CH1-DEF, CH2-DEF and CHn-DEF, via a first telecommunications network (a high speed television broadcast network customarily using satellite or fiber optic cable). The input CH1-DEF to video switch VS.sub.1 identifies that the programmed channel video signal CH1 is the default (DEF) signal for that video switch. A stream of commercial inserts (CI) is also applied to each video switch, as well as a third, locally generated video signal which is a single frame (S.Fr.) video signal. The commercial insert video signal is received by the cable system operator via a second high speed telecommunications network along with a series of video switch commands (Sw.Comm.). Accordingly, each video switch in the Perine receives a respective programmed channel video composite signal, a commercial insert video composite signal and a local generated, single frame (S.Fr.) signal.
Each respective video switch is controlled by first, second and third switch commands respectively corresponding to a programmed channel switch command, a commercial insert switch command and a local video switch command. These commands are applied to each switch on a per switch basis (Sw.Comm.1; Sw.Comm.2; Sw.Comm.n) in accordance with the stream of commands coming from a remote location and via the second telecommunications network. As described in greater detail in the Perine patent, at the remote location, each programmed channel is monitored and certain audio indicators are sensed to determine when a local avail is approaching. A computer at the remote location notes the beginning and the end of each commercial segment in the generally continuous sequential stream of commercial inserts (CI) broadcast to the cable system operator over the second telecommunications network. If a local avail for a particular programmed channel coincides with the beginning of a local avail, the computer at the remote location generates a switch command for a particular video switch thereby commanding the switch to change its state and switch from the default (CH1-DEF) to the commercial insert (CI) at a particular time t. If the local avail begins at an intermediate time during a commercial insert (CI) segment of the CI stream, the computer at the remote location generates a switch command changing the state of the switch (VS.sub.1) to apply the single frame (S.Fr.) video signal to its output (V.OUT) until the beginning of the next CI segment at which time the remote computer generates the appropriate switch command thereby changing switch VS.sub.1 to insert the stream of commercial inserts at that switch over time t. Each video switch in the Perine patent includes a frame blanking (F.BLK.) circuit device which blanks the output of the switch for a certain period of time such that the inserted video signal (either the default, the CI, or the single frame insert) can be synchronized or timed with the programmed channel video signal. As an additional feature, the video switch includes character generators (CH.GEN.) with which the cable system operator can overlay characters onto the composite video signal. Node A in FIG. 1 simply shows that the video switch handles three video inputs and selects one of those video inputs as an output based upon the remotely generated switch commands.